A library for generating printable, high quality maps in the browser.

Usage no npm install needed!

<script type="module">
  import camptocampInkmap from 'https://cdn.skypack.dev/@camptocamp/inkmap';


inkmap, a library for generating high resolution maps in the browser
Live demo here!


inkmap is based on OpenLayers and will generate maps in PNG format based on a given JSON specification.

inkmap can handle long-running jobs (e.g. A0 format in 300 dpi) and provides an API for following a job progress. It uses a service worker in the background provided the user browser supports OffscreenCanvas, and falls back (almost) seamlessly to the main thread if not.

Please note that inkmap has been entirely funded and supported by the French Ministry of Ecology as part of their Descartes web mapping toolkit, hosted here: https://adullact.net/projects/descartes/



To include the library in your project:

$ npm install --save @camptocamp/inkmap

Then import the different methods from the inkmap package:

import { print, downloadBlob } from '@camptocamp/inkmap';

  layers: [ ... ],
  projection: 'EPSG:4326',


inkmap offers advanced job monitoring through the use of Observables provided by the rxjs library.

Observables are different from Promises in that they can emit multiple values instead of just one, and are a very good fit for progress reporting.

To use an Observable, simply call its subscribe() method with a function as argument. The function will be called anytime a new value is emitted, like so:

import { getJobStatus } from '@camptocamp/inkmap';


getJobStatus(jobId).subscribe((jobStatus) => {
  // do something with the status

Note that for long-lived Observables (i.e. Observables that never completes) it is important to call unsubscribe() when the emitted values are not needed anymore. Open subscriptions to Observables might create memory leaks.

Enabling the service worker

inkmap can and will use a dedicated service worker for running print jobs if given the chance. This offers the following advantages:

  • Jobs run in a separate thread, meaning the user navigation will not be impacted at all by any CPU-intensive task
  • The service worker isn't tied to a window or tab, so jobs will continue running when the tab is closed (and even when the browser is closed, depending on the platform)
  • Push notifications might be sent to the user when a print job complete (not implemented yet)

To enable this, the inkmap-worker.js file located in the dist folder must be published on the same path as the application using inkmap.

The worker file can be published either using a symbolic link or by actually copying the file, for example in the application build pipeline.

If using Webpack to build the application, a solution is to use the CopyWebpackPlugin:

module.exports = {
  plugins: [
     new CopyWebpackPlugin([
         from: 'node_modules/@camptocamp/inkmap/dist/inkmap-worker.js',
         to: 'dist'


Important note: all API functions are named exports from the inkmap package.

print(jsonSpec: PrintSpec): Promise<Blob>

Takes in a PrintSpec object and returns a Promise which resolves to a Blob containing the final image.

queuePrint(jsonSpec: PrintSpec): Promise<number>

Takes in a PrintSpec object and returns a Promise which resolves to a job id (number) immediately.

getJobStatus(id: number): Observable<PrintStatus>

Takes in a job id and returns an Observable which will regularly emit PrintStatus objects, and complete when the final image was generated.

cancelJob(id: number): void

Takes in a job id, cancel the job and cease all requests immediately.

getJobsStatus(): Observable<PrintStatus[]>

Returns a long-running observable which emits an array of print job status. Once a job is finished it will appear once in the array and then will not be part of subsequent emissions.

Note: This observable will never complete. Don't forget to unsubscribe!

registerProjection(definition: ProjectionDefinition): void

Takes in a projection definition and registers it with proj4.

getAttributionsText(spec: PrintSpec): string

Returns the full attributions text of the spec.

getNorthArrow(spec: PrintSpec, sizeHint?: [number, string]): PrintableImage

Returns a PrintableImage containing the north arrow for the given spec. The image will be square and have the same DPI as the spec. A sizeHint (e.g. [3, 'cm']) can be provided to request a larger or smaller arrow. Supported size units are the same as in the PrintSpec type.

getScaleBar(spec: PrintSpec, minimumWidth?: [number, string]): PrintableImage

Returns a PrintableImage containing the scale bar for the given spec. The image will have the same DPI as the spec. A minimumWidth (e.g. [80, 'mm']) can be provided to request a smaller or larger scale bar. Supported size units are the same as in the PrintSpec type.

Note that for this scale bar to be relevant in a printed document, its real-world size has to be respected.

PrintSpec type

A PrintSpec object describes the content and aspect of the map to be printed.

field type description
layers Layer[] Array of Layer objects that will be rendered in the map; last layers will be rendered on top of first layers.
size [number, number] or [number, number, string] Width and height in pixels, or in the specified unit in 3rd place; valid units are px, mm, cm, m and in.
center [number, number] Longitude and latitude of the map center.
dpi number Dot-per-inch, usually 96 for a computer screen and 300 for a detailed print.
scale number Scale denominator.
scaleBar boolean \| ScaleBarSpec Indicates whether scalebar should be printed (true). Also allows to pass options object: {"position": "bottom-left", "units": "metric" } (default values). Possible values are:
  • position: "bottom-left" \| "bottom-right"
  • units: "degrees" \| "imperial" \| "metric" \| "nautical" \| "us" (same as ol.control.ScaleLine)
northArrow boolean \| string North arrow position; either 'top-left', 'bottom-left', 'bottom-right' or 'top-right'; true defaults to 'top-right'; absent or false means not to print the north arrow.
projection string Projection name. If starting with EPSG:, and other than EPSG:3857 or EPSG:4326, definition will be downloaded on [https://epsg.io/].
projectionDefinitions [projectionDefinition] Optional. Registers new projections from the definitions.
attributions boolean \| string Position of the attributions to be printed on the map; either 'top-left', 'bottom-left', 'bottom-right' or 'top-right'; if not defined, attributions will not be printed.

Layer type

A Layer object describes a layer in the printed map.

field type description
type string Either XYZ, WMTS, WMS, WFS or GeoJSON.
url string URL or URL template for the layer; for XYZ layers, a URL can contain the following tokens: {a-d} for randomly choosing a letter, {x}, {y} and {z}.
opacity number Opacity, from 0 (hidden) to 1 (visible).
attribution string Attribution for the data present in the layer.

WMS layer type

Additional options for WMS layer type.

field type description
layer string Layer name.
version string Version of WMS protocol used: 1.1.1 or 1.3.0 (default).
tiled boolean Indicates whether the WMS layer should be requested as tiles. Defaults to false.

WMTS layer type

Additional options for WMTS layer to define the layer source. See https://openlayers.org/en/latest/apidoc/module-ol_source_WMTS-WMTS.html for the full list of options. The following table introduces the common options to use.

field type description
requestEncoding string Request encoding: KVP, REST.
format string Image format. Only used when requestEncoding is 'KVP'. eg image/png.
layer string Layer name as advertised in the WMTS capabilities.
style number Style name as advertised in the WMTS capabilities.
projection string Projection.
matrixSet string Matrix set.
tileGrid TileGrid TileGrid object, see https://openlayers.org/en/latest/apidoc/module-ol_tilegrid_TileGrid-TileGrid.html for options

WFS layer type

Additional options for WFS layer type.

field type description
layer string Layer name.
version string Version of WFS protocol used: 1.0.0, 1.1.0 (default) or 2.0.0.
format string Format used when querying WFS, gml (default) or geojson. inkmap determines the GML parser based on the WFS version used.
style object JSON object in geostyler notation, defining the layer style.

GeoJSON layer type

Additional options for GeoJSON layer type.

field type description
geojson object Feature collection in GeoJSON format; coordinates are expected to be in the print job reference system.
style object JSON object in geostyler notation, defining the layer style.

projectionDefinition type

A projectionDefinition object describes a projection to be registered in proj4.

field type description
name string Name of the projection, written as prefix:code.
bbox [number, number, number, number] Extent of the projection, written as [maxlat, minlon, minlat, maxlon].
proj4 string Proj4 definition string.

PrintStatus type

A PrintStatus object describes the status of a print job.

field type description
id number Job id.
progress number Job progress, from 0 to 1.
status string Either 'pending', 'ongoing', 'finished' or 'canceled'.
resultImageUrl string An URL used to access the print result (PNG image). This will only be available once the job status is 'finished'.

PrintableImage class

A PrintableImage is essentially a wrapper around a native image or canvas, with added information about its real world size.

method return type description
getImage() HTMLImageElement or HTMLCanvasElement Returns the native image to be drawn or printed.
getRealWorldDimensions(units: string) [number, number] Returns the real world dimensions of the image for a given unit (e.g. mm).
getDpi() number Returns the image DPI.


Under the hood, inkmap will attempt to install a service worker on the page it is called. The service worker will then be in charge of loading all the map images and data, composing them together and giving them back to the application code.